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Temperature Compensation for a Meade 12" LX850 f/8 ACF

Meade SCT
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#1 lmclouth

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Posted 21 September 2021 - 03:54 PM

Hello,

 

I'm getting a Rigel Systems nSTEP autofocuser for my Meade 12" LX850 f/8 ACF OTA.

Does anyone know the temperature coefficient or how far to move for 1 degree C of temperature change?

 

Thanks,

 

Lamar

 



#2 carolinaskies

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Posted 21 September 2021 - 06:32 PM

You should ask this in the equipment forum for probably the best answer.  Search in that forum for NStep related threads and you'll probably find several discussions over the years. 

I believe it is going to depend on the focal length and how you use the NStep itself and likely will be a trial and error over a few sessions to see the effect of differing increments.  



#3 rigelsys

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Posted 21 September 2021 - 09:23 PM

It is really something one has to figure out by experiment.  



#4 AF7JQ

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Posted 21 September 2021 - 09:44 PM

My LX600 12" (same OTA as LX850) with the Optec Direct Sync ACF focuser seems to like 144 steps per degree C drop. The stepper motor moves 1.1micron per step. The OTA changes focus a lot as the temps fall during an imaging session. Before getting the focuser I would have to refocus about every 15-20 minutes.



#5 AF7JQ

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Posted 21 September 2021 - 09:55 PM

Also, I just looked at the focuser you mentioned...looks to be a huge amount of back focus space taken up. You might try to see if anyone else has used that focuser with a LX850 F/8 OTA. F/8 OTA's don't have near the same amount of back focus space as an F/10 OTA of the same size.The Optec Direct Sync Focuser mounts to the focus knob and is not in the optical path. F/8 OTA's have very little mirror flop compared to other F/10 scopes so putting the focuser on the knob instead of the optical path works great!



#6 lmclouth

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Posted 21 September 2021 - 10:08 PM

Also, I just looked at the focuser you mentioned...looks to be a huge amount of back focus space taken up. You might try to see if anyone else has used that focuser with a LX850 F/8 OTA. F/8 OTA's don't have near the same amount of back focus space as an F/10 OTA of the same size.The Optec Direct Sync Focuser mounts to the focus knob and is not in the optical path. F/8 OTA's have very little mirror flop compared to other F/10 scopes so putting the focuser on the knob instead of the optical path works great!

Yes, I was interested in the Optec DirectSync ACFX #19975 but the $595+ price tag was way too much.

 

The nSTEP attaches to the coarse focus knob, so it doesn't take up any back focus space.



#7 dcaponeii

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Posted 22 September 2021 - 01:34 PM

Also, I just looked at the focuser you mentioned...looks to be a huge amount of back focus space taken up. You might try to see if anyone else has used that focuser with a LX850 F/8 OTA. F/8 OTA's don't have near the same amount of back focus space as an F/10 OTA of the same size.The Optec Direct Sync Focuser mounts to the focus knob and is not in the optical path. F/8 OTA's have very little mirror flop compared to other F/10 scopes so putting the focuser on the knob instead of the optical path works great!


I’m using an old JMI NGF-S focuser and do not have any trouble reaching focus even with a Barlow installed. My scope is the 12” f/8 ACF from Meade

#8 lmclouth

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Posted 22 September 2021 - 04:10 PM

It is really something one has to figure out by experiment.  

And how do you perform that experiment?

 

Do you have to see the current temperature and use a Bahtinov Mask to first make focus.  Then watch for the temperature to drop a certain amount (like 1 or 2 degrees C) and then put the OTA back into focus and remember the number of steps it took?

 

Or is there a better method?




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